Project RESUN, a Radio EVLA Search for UHE Neutrinos

In the past decade there have been several attempts to detect Ultra High Energy (UHE) neutrinos via radio Ĉerenkov bursts in terrestrial ice or the lunar regolith. So far these searches have yielded no detections, but the inferred flux upper limits have started to constrain physical models for UHE neutrino generation. We report results from the Radio EVLA Search for UHE Neutrinos (RESUN) experiment, aimed at further limiting isotropic and point-source production models. RESUN uses the Expanded Very Large Array (EVLA) configured in multiple sub-arrays of four antennas observing at 1.4 GHz and pointed along the lunar limb to detect cm-wavelength Ĉerenkov bursts. No pulses of lunar origin exceeding a threshold of 0.017 μV m−1 MHz−1 were detected during a observing campaign totaling 200 h. The RESUN null detection implies an upper limit to the differential isotropic neutrino flux EdN/dE < 1 km−2 yr−1 sr−1 at 90% confidence level for sources with energy (E) exceeding 1021.2 eV and EdN/dE < 0.1 km−2 yr−1 sr−1 for E > 1022.5 eV. The isotropic flux upper limit is the lowest published for lunar searches in the range 1020.7 eV < E < 1022.3 eV and is inconsistent with extragalactic and halo Z-burst models for neutrino generation, in agreement with the ANITA Antarctic ice observations and WMAP neutrino mass estimates. Further, we establish 90% confidence differential flux limits for selected AGN sources located along the lunar celestial path.